mntns: Add a limit on the number of mount namespaces.

v2: Fixed the very obvious lack of setting ucounts
    on struct mnt_ns reported by Andrei Vagin, and the kbuild
    test report.

Reported-by: Andrei Vagin <avagin@openvz.org>
Acked-by: Kees Cook <keescook@chromium.org>
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>

4 files changed, 24 insertions, 1 deletions

diff --git a/fs/mount.h b/fs/mount.h
index 14db05d424f7..e037981d8351 100644
--- a/fs/mount.h
+++ b/fs/mount.h
@@ -10,6 +10,7 @@ struct mnt_namespace {
         struct mount *  root;
         struct list_head        list;
         struct user_namespace   *user_ns;
+        struct ucounts          *ucounts;
         u64                     seq;    /* Sequence number to prevent loops */
         wait_queue_head_t poll;
         u64 event;
diff --git a/fs/namespace.c b/fs/namespace.c
index 7bb2cda3bfef..491b8f3e4c9a 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -2719,9 +2719,20 @@ dput_out:
         return retval;
 }
 
+static struct ucounts *inc_mnt_namespaces(struct user_namespace *ns)
+{
+        return inc_ucount(ns, current_euid(), UCOUNT_MNT_NAMESPACES);
+}
+
+static void dec_mnt_namespaces(struct ucounts *ucounts)
+{
+        dec_ucount(ucounts, UCOUNT_MNT_NAMESPACES);
+}
+
 static void free_mnt_ns(struct mnt_namespace *ns)
 {
         ns_free_inum(&ns->ns);
+        dec_mnt_namespaces(ns->ucounts);
         put_user_ns(ns->user_ns);
         kfree(ns);
 }
@@ -2738,14 +2749,22 @@ static atomic64_t mnt_ns_seq = ATOMIC64_INIT(1);
 static struct mnt_namespace *alloc_mnt_ns(struct user_namespace *user_ns)
 {
         struct mnt_namespace *new_ns;
+        struct ucounts *ucounts;
         int ret;
 
+        ucounts = inc_mnt_namespaces(user_ns);
+        if (!ucounts)
+                return ERR_PTR(-ENFILE);
+
         new_ns = kmalloc(sizeof(struct mnt_namespace), GFP_KERNEL);
-        if (!new_ns)
+        if (!new_ns) {
+                dec_mnt_namespaces(ucounts);
                 return ERR_PTR(-ENOMEM);
+        }
         ret = ns_alloc_inum(&new_ns->ns);
         if (ret) {
                 kfree(new_ns);
+                dec_mnt_namespaces(ucounts);
                 return ERR_PTR(ret);
         }
         new_ns->ns.ops = &mntns_operations;
@@ -2756,6 +2775,7 @@ static struct mnt_namespace *alloc_mnt_ns(struct user_namespace *user_ns)
         init_waitqueue_head(&new_ns->poll);
         new_ns->event = 0;
         new_ns->user_ns = get_user_ns(user_ns);
+        new_ns->ucounts = ucounts;
         return new_ns;
 }
 
diff --git a/include/linux/user_namespace.h b/include/linux/user_namespace.h
index c6bc980b06a9..30ffe10cda18 100644
--- a/include/linux/user_namespace.h
+++ b/include/linux/user_namespace.h
@@ -30,6 +30,7 @@ enum ucount_type {
         UCOUNT_UTS_NAMESPACES,
         UCOUNT_IPC_NAMESPACES,
         UCOUNT_NET_NAMESPACES,
+        UCOUNT_MNT_NAMESPACES,
         UCOUNT_CGROUP_NAMESPACES,
         UCOUNT_COUNTS,
 };
diff --git a/kernel/ucount.c b/kernel/ucount.c
index 205f1a07faac..9d20d5dd298a 100644
--- a/kernel/ucount.c
+++ b/kernel/ucount.c
@@ -72,6 +72,7 @@ static struct ctl_table user_table[] = {
         UCOUNT_ENTRY("max_uts_namespaces"),
         UCOUNT_ENTRY("max_ipc_namespaces"),
         UCOUNT_ENTRY("max_net_namespaces"),
+        UCOUNT_ENTRY("max_mnt_namespaces"),
         UCOUNT_ENTRY("max_cgroup_namespaces"),
         { }
 };